The Japanese government may have underestimated by 20 percent the internal radiation doses in workers during the initial phases of the Fukushima No. 1 nuclear power plant disaster, a U.N. panel said.
The Japanese government may have underestimated by 20 percent the internal radiation doses in workers during the initial phases of the Fukushima No. 1 nuclear power plant disaster, a U.N. panel said.
The U.N. Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) raised doubts about the dose estimates of the Japanese government and Tokyo Electric Power Co., the plant operator, in a summary of a report submitted to the Fourth Committee of the U.N. General Assembly on Oct. 12.
UNSCEAR used data provided by the Japanese government, TEPCO and other entities to assess the amount of radioactive substances discharged during the nuclear crisis that began in March 2011. It also analyzed radiation doses in the 25,000 or so individuals who worked at the plant no later than October 2012.
The U.N. committee noted that workers were tested for thyroid gland doses from radioactive iodine only after a significant delay. It also said the dose assessment procedures totally ignored iodine-132 and iodine-133, which have short half-lives of 2 hours and 20 hours, respectively.
After assessing discharge volumes and their contribution to doses for each class of radioactive substance, UNSCEAR concluded that worker doses during the early stages of the nuclear crisis may have been underestimated by about 20 percent.
The government and TEPCO are providing free health checkups to Fukushima plant workers whose doses have reached certain levels.
Currently, about 1,100 individuals who received 50 millisieverts or more in whole-body doses can receive free tests for cancer of the thyroid gland, lungs, stomach and colon. About 2,000 people with whole-body doses below 50 millisieverts but thyroid gland doses of 100 millisieverts or more are qualified to be tested for thyroid gland cancer.
If UNSCEAR’s assessment is accurate, more workers should be eligible for the health checkups. The panel plans to finish and release the report by year-end at the earliest.
But the possible underestimates are just one problem in a system that has proved inefficient in protecting workers’ health.
Long-term observations are needed to fully understand the risk from radiation exposure among workers at the plant. But many companies involved have failed to conduct medical examinations or file reports to the government--even though they are required to do so under law.
A government database on workers’ health conditions is still not running, making it impossible to check whether workers have suffered health problems.
The health ministry has required companies to submit medical examination results for 20,000 people who worked at the Fukushima No. 1 plant before December 2011, depending on the level of their radiation doses.
The ministry wanted to use the results to create a database and set up a framework to check whether workers have developed cancer, cataracts and other diseases.
However, by August, companies had failed to submit basic examination data on 4,297 workers, more than one-third of all the people who should be covered.
The health ministry ordered TEPCO and 81 primary contractors to submit the data. It is still waiting for that information.
Some companies are believed to have not even conducted the health examinations.
A more serious problem is that experts cannot check all thyroid examination results.
The database covers whole-body dose data and examination results of lung, colon and other cancers, among other items. But it does not cover thyroid dose data, and only part of the thyroid examination results is included.
An expert criticized incomplete results, saying radiation exposure in the Fukushima nuclear disaster came in large part from radioactive iodine, which tends to accumulate in the thyroid gland.
(This article was compiled from reports by Yuri Oiwa and Toshio Tada.)